1. Field of the Invention
This invention relates to a spinneret device for conjugate fibers of eccentric sheath-and-core type. More particularly it relates to a spinneret device for spinning two kinds of spinning stocks into sheath-and-core type conjugate fibers.
2. Description of the Related Art
Spinneret devices conventionally employed for producing conjugate fibers of eccentric sheath-and-core type have been sometimes almost the same as those having a spinneret for conjugate fibers of concentric sheath-and-core type. A spinneret for conjugate fibers of concentric sheath-and-core type is a circular spinneret device which is composed of a nozzle plate provided with spinning holes for melt-spinning of sheath-and-core conjugate fibers and a distributing plate provided with introducing holes, for distributing a core component and a sheath component into the spinning holes. A space or zone which is not so narrow is formed between the back surface of the nozzle plate and the lower or frontal surface of the distributing plate. The spinning holes and the core component-introducing holes are each arranged in a circular form having the same diameter, and the sheath component-introducing holes are bored either on the inner side or on the outer side of the circular form of the core component-introducing holes. Further, in order to form a small clearance between the core component-introducing holes and the spinning holes, either one of the core component-introducing holes or the spinning holes has a flat surface projection, or the respective core component-introducing holes has a single projection which is inserted into the inlet of the spinning hole. Thus, the core component is individually introduced into the respective spinning holes, and the sheath component staying in the small clearance zone is introduced into the respective spinning holes in a radial form to form conjugate fibers of sheath-and-core type, which are then spun out through the spinning holes.
In order to spin conjugate fibers of concentric sheath-and-core type by means of such a spinneret device, core component-introducing holes and spinning holes are positioned concentrically, while when conjugate fibers of eccentric sheath-and-core type are spun, the distributing plate or the nozzle plate is moved by rotation or angle-displacement so that the core component-introducing holes and the spinning holes are positioned on an optional eccentric axis, and fixed. As to a degree of the eccentricity at that time, there is employed a method of varying an angle of the rotation of the circular arrangement of the core component-introducing holes or the circular arrangement of the spinning holes on the same axis or an eccentric axis thereof.
It is possible to obtain conjugate fibers of concentric or eccentric sheath-and-core type with no problem in the case of a spinneret having a relatively small number of spinning holes arranged in a spinneret. However, if many spinning holes are intended to be arranged, it is impossible to obtain conjugate fibers of concentric or eccentric type having a good uniformity.
Namely, a number of processing steps are not only required for precision cutting for providing projections, resulting in a highly expensive device, but also when the circular arrangement of the core component-introducing holes and that of the spinning holes are subjected to angle-displacement on the same axis, this is possible in the case of only one circular arrangement, but when the above circular arrangements are subjected to angle-displacement on eccentric axis, this is limited by the size of the inlets of spinning holes; hence a precise eccentric cum or a precise boring processing at the eccentric site is required. Further, it is practically impossible to ensure even a space of providing the projections, and also it is difficult to make the density of the spinning holes 5 holes/cm.sup.2 or more.
Further, when the clearance between the core component-introducing holes and the spinning holes is narrowed, since the spinneret of the above-mentioned structure allows the sheath component to flow in the periphery of the spinning holes by the flow resistance of the sheath component which occurs in the narrowed clearance zone, the area of the projections should be reduced in order to arrange the spinning holes more densely, and the clearance between the nozzle plate and the back plate in the zone should be more narrowed. Thus there are raised various problems such as contaminants in the spinning stocks are liable to hinder the flow of spinning liquid, and that a long-term or stabilized spinning is not only difficult to be carried out, but also fine projections on the surfaces of the nozzle plate and the back plate are liable to be injured during operations of washing and assembling, to shorten its life.
Further, in the case of spinning conjugate fibers of eccentric sheath-and-core type, it has generally been necessary to reduce the clearance of the narrow zone, when the viscosity of the sheath component polymer is low, while necessary to increase the clearance, when the viscosity is high.
Further, the clearance should be set to an optimum value based upon various spinning conditions such as the kinds and combinations of polymers used as the core component and the sheath component, spinning temperature, the quantity of the polymers extruded, etc. Thus, in the case of conventional spinneret devices having a fixed clearance in the narrow zone, it has been necessary to employ different spinneret devices each time these conditions are changed.
As a device for solving the above-mentioned problems, the present inventors have proposed a spinneret device disclosed in Japanese patent application laid-open No. Sho 62-37126/1987. However, this device is directed to a device for producing conjugate fibers of concentric sheath-and-core type; thus it has been impossible to produce conjugate fibers of eccentric sheath-and-core type using the device.